You'd certainly need to find the right doctor, though. Not many doctors are well-versed in this subject and they might just say "oh it is just a side effect of the hallucinogens"... even if it isn't.
The thing is though, even if it is all in the head of the person who claims he/she has HPPD, it is irrelevant. Before they took the drug they didn't notice the effects. After taking the drug they did notice them and as a result they may be anxious. (Even if the effects were there all along). If that is the case maybe this problem can be solved by education, information that they should know before ever taking psychedelics.
The visual cortex is an extremely complex beast. It isn't a matter of just oh your eyes pick up the photons and you see. There are different parts of the brain that trace the outlines of objects, different parts that fill in objects, decode text, neurons that detect motion, etc. All these aspects of the visual cortex are obviously influenced when you take psychedelics. (And I'm not saying it isn't beautiful and magical, it is)
Normal people might look at say a picture, and then turn away and see a positive afterimage for a flicker of a split second. People who claim to have HPPD claim to see afterimages for up to several seconds, all the time. This is not normal. Yes this happens in people who have never taken psychedelics and it is called palinopsia. Maybe some people are predisposed to this condition and psychedelics can trigger it, similar to how they can trigger latent schizophrenia.
If I sound wishy-washy on this subject, it is because I am. Until there is more research done in this area I don't see how anyone can definitively say it exists or it doesn't, much less pass judgment on those who say they are affected by it. There never was any active research into this phenomenon in the 20th century, an era during which as I recall, a lot of today's accepted illnesses such as allergies were considered to be "all in the head" by the medical profession.
